It has been recognized for some time that walking is one of the best exercises that a person can perform for therapy and general fitness, if conducted on a regular and continued basis. People who are in good health and physically fit can maintain their condition by regular walking; those who are not physically fit can often significantly improve their fitness and overall physical condition by walking. Walking is also regularly prescribed by physicians for people recovering from surgery or major illnesses such as heart attacks. Walking has an advantage that it can be a low to moderate energy exercise. Also, walking motions are natural to the body, unlike exercises such as rowing, bicycling or nordic skiing. It has been found that if a person is allowed to select his walking pace, he can walk comfortably for a much longer time than he could row, cycle or ski.
Unfortunately, for many reasons most people do not walk regularly for exercise. Perhaps one has a physical infirmity, such as paralysis or loss of a limb. Other reasons may be environmental: people usually do not wish to walk where streets are busy, unsafe, unlighted or do not contain an appropriate sidewalk or footpath for walkers. Finally, even people who would otherwise walk regularly often find their ability to take walks curtailed because of inclement weather, time schedule conflicts or similar reasons.
Ordinary walking has some detrimental aspects. The weight bearing joints (feet, ankles, knees, hips and spine) can be considered to be the "limiting factor" in walking for exercise or therapy. Generally in walking these are the joints which become fatigued because of the stress placed on them at each step. Of course, a person whose feet, ankles, etc. are tired will be unable or unwilling to do more walking, regardless of the generally good condition of the rest of his body.
Also, when one walks he is of course upright and the spinal column is subject to maximum axial gravitational loading. Each step taken imparts vibration and stress to the spinal column. For all walkers the combination of axial gravitational loading, stress and vibration will accelerate the onset of spinal fatigue. In addition, for those with spinal, back or muscle problems, the axial gravitational loading, vibration and stress frequently produce significant pain, such that walking is difficult or impossible.
It would therefore be advantageous to have a device which a person could use indoors and at convenient times and which would allow him to perform the same movements as ordinary walking to obtain the benefits therefrom but without detrimental effects on the spine and feet.
In the past there have been numerous devices described in the literature and patents which have been said to provide walking exercise. Some have simply been treadmills or nordic skiing devices. More pertinent herein are the variety of prior art "walking simulators." A review of typical devices of this type reveals, however, that it has been common to describe virtually any kind of manipulation of the arms and legs, whether in unison or separately, as "simulated walking". Representative of the prior art devices is the device shown in U.S. Pat. No. 3,596,654 in which the arms are moved up and down in the frontal plain in a "wing flapping" motion. Numerous other machines which move the arms and legs are designed to simulate swimming motions, which, of course, require an entirely different set of arm and leg motions from walking. Other devices, such as that shown in U.S. Pat. No. 2,681,650, cause the limbs to be moved in approximately the correct orientation, but the structure is principally designed to provide passive motorized motion to users, such as polio patients, who have little or no use of their limbs. There is only limited provision for a user to initiate movement himself, and such as there is against virtually no resistance so that it can be used by severely crippled individuals for very short periods of time. A related class of devices is exemplified by U.S. Pat. No. 3,060,926 which provides independent and uncoordinated motion to the separate limbs or parts of limbs for users who have no ability to move those limbs. There is no provision for any user initiated motion or for coordinated or multifunctional movement of the limbs.
It would therefore be advantageous to have a device which is multifunctional and can be used equally well by both fit and infirm individuals to perform fully coordinated walking movements. It would also be advantageous to have such a device capable of adjustment so that it could operate over the entire range of effort on the part of the user.